The following problems are observed when using Heimdal's libgss/kerberos impl:
1. It reports BAD_MECH error when passing in OID which are created by 3rd parties, e.g.
through DER encoding. This is different from SEAM and MIT which can recognize OIDs
created by the caller.
2. After context is exported, it resets the context handle to 0 automatically.

The current native provider impl needs to adjust accordingly to work with Heimdal's
impl.